1. Field of Invention
This invention relates to teleconferencing systems. More particularly, the invention relates to audio teleconferencing systems which create a sound field effect of participants about a virtual conference table.
2. Description of the Prior Art
In today's environment, many businesses rely heavily on audio teleconferencing to conduct multi-party discussions from remote locations. These teleconferences are typically scheduled with the telephone company which reserves the required number of ports or incoming lines on an audio conference bridge located at a telephone company's switching office.
In the past few years, much attention has been paid to improving the conference speaker phones used in large conference rooms. These improvements have been built in to the conference room phones to help cancel room echoes, discriminate between several people speaking from different locations in the room, canceling feedback, and automatically enhancing the voice signal for optimal intelligibility. These improvements have been based on using a Digital Signal Processor (DSP) in the conference phone units or their supporting equipment. DSP's are, by design, software or firmware platforms for processing various analog signals such as voice and video waveforms. Thus, conference speaker phones have become software driven computer systems that specialize in encoding and decoding audio waveforms.
In order to create a more realistic sense of a virtual conference among the participants, a need exists to add a sound field effect to the conference phone capability to create a sense of spatial location among the participants, as if all the teleconference participants were seated around a virtual conference table.
Prior art related to teleconferencing with sound field effect is as follows:
U.S. Pat. No. 4,658,425 issued Apr. 14, 1987, discloses a microphone and loudspeaker arrangement for use in a teleconference system wherein a plurality of microphones are held in a fixed relationship to a loudspeaker. The microphones are independently gated ON in response to (1) speech picked up by the microphone, (2) a loudspeaker signal driving the loudspeaker, and (3) an electrical signal related to the microphone signal of the other associated microphones. A noise adapting threshold circuit generates a voltage level representative of background noise which is compared with the microphone signal of a respective microphone for determining whether the microphone is receiving speech. A decisional circuitry monitors the microphone signal of the associated microphone with respect to a MAX bus which carries microphone signals representative of the level of the microphone signals at the other microphones. The decisional circuitry generates a signal indicating that the associated microphone is the first loudest microphone signal.
U.S. Pat. No 4,734,934, issued Mar. 29, 1988, discloses a teleconferencing bridge which simulates the auditory spatial ambience of a face-to-face conference. The bridge uses a binaural approach to simulate spatial ambience.
U.S. Pat. No. 5,020,098, issued May 28, 1991, discloses a high-fidelity audio telephone conferencing arrangement which provides talker position information. Digitized high-fidelity audio is combined with digitized phase information, derived from talker position detecting circuitry in a local telephone station. The digitized high-fidelity audio is transmitted over the telephone channel to one or more remote telephone stations. A receiver in each remote station decodes the digital information and provides the high-fidelity audio signal to multiple spatially separated acoustic output devices. The digitized pulse information controls "panning" of the audio signal among the acoustic output devices. By varying the level of audio signal flowing to each acoustic device, the position of the talker can be created in a specific position in the remote listener sound field and the talker's identity thereby more easily determined. In addition, talker location information may be shared among multiple telephone stations participating in a telephone conference. Information as to the location of the talker along with the position of the talker is provided to each remotely located telephone station. The location of the talker is represented by the audio signal occurring in a designated general area of the remote listener's sound field and the position of the talker is represented by the creation of the audio signal in a specific position in this general area.
U.S. Pat. No. 5,335,011 issued Aug. 2, 1994, discloses a sound localization system for teleconferencing using self-steering microphone arrays. A microphone array covers a particular field which is divided into fixed, non-overlapping volume zones or sectors. Using the microphone array, when a sound is detected its source is located and a highly-directional beam is formed in the sector or zone containing the source of the sound. Only one beam is formed at any instant depending upon the location of the source of the sound. Thus, ambient noise, room reverberation, and acoustic coupling are greatly reduced. In addition to enhancing speech quality and reducing reverberation, noise and acoustic coupling the microphone array is capable of outputting a digital signal indicating which volume zone contains the source of the sound.
U.S. Pat. No. 5,619,555, issued Apr. 8, 1997, discloses an audio conferencing system in which conference participants interface with the system through a Graphical User Interface (GUI) computer program running on a remote computer or workstation. To join an audio conference in progress, a participant controls a GUI computer program to transmit a signal over a local area network to a central server. The central server, by examining database information, determines whether the participant is authorized to join the audio conference. If so, the central server controls a telephone system connected thereto and causes the telephone system to call the participant at a prelisted telephone number. The participant then joins the actual audio conference merely by answering the telephone.
None of the prior art discloses adding an audio imaging sound field to a conference phone to create a sound field effect of telephone conference participants using standard telephones and seated about a "virtual conference table" without the need for a telephone conference bridge to support the standard telephone on the conference.